This invention relates to a multiplex motor control system which prevents a motor from being operated for an excessive time period.
Modern automotive vehicles include a number of electric motors which are under either manual or automatic control. Such motors are used for example to control the position of outside mirrors, car windows, power seats, power radio antennas, and the like. In each case, the motor is connected to the driven object by a linkage and operates to drive the linkage to move the driven object between two limits of travel.
Often, such motors can be abused by an operator who commands motor activation for an excessively long time period. Of course, when the driven object reaches its extreme position, further movement is not possible. Some means must be provided to prevent damage to the motor and the drive linkage.
One prior art approach to this problem is to provide a drive linkage which allows the motor to run without moving the driven object. Such linkages are conventionally used in power mirrors. Another approach of the prior art is to sense the current drawn by the motor or the torque exerted by the motor, and automatically to deactivate the motor if the motor torque exceeds a predetermined value.
For some time there has been an interest in applying multiplex systems to control the components of vehicles such as automobiles. Britain U.S. Pat. No. 4,293,947 is one example of such a multiplex system. In spite of this interest, currently available vehicle multiplex systems do not fully exploit the potential of such systems for providing improved control functions in vehicles.